percpu: perform tlb flush after pcpu_map_pages() failure

commit 849f5169 upstream.

If pcpu_map_pages() fails midway, it unmaps the already mapped pages.
Currently, it doesn't flush tlb after the partial unmapping.  This may
be okay in most cases as the established mapping hasn't been used at
that point but it can go wrong and when it goes wrong it'd be
extremely difficult to track down.

Flush tlb after the partial unmapping.
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

mm/percpu-vm.c

@@ -273,6 +273,7 @@ static int pcpu_map_pages(struct pcpu_chunk *chunk,
 		__pcpu_unmap_pages(pcpu_chunk_addr(chunk, tcpu, page_start),
 				   page_end - page_start);
 	}
+	pcpu_post_unmap_tlb_flush(chunk, page_start, page_end);
 	return err;
 }